Process for producing crystalline polyolefins in the presence of an aluminum trialkyl, transition metal halide, and an esterified polyhydric alcohol



United States Patent anagram PRQCESS F9 2 PRQDUCENG QRYSTALLINE PGZLY- OLEFENS EN THE PRESENiIE OF AN ALUME UM TRIALKYL, TRANdiTIGN METAL HALEDE, AND Ais ESTERZEEED PGLYEEYDMC ALCOHUL Harry W. Cont er, in, and Frederick R. Eoyner, Kingsport,

Tenn, assignors to Eastman Kodak Qompany, Rochester, N.Y., a corporation of New Jersey No Drawing. Filled Mar. 1, 1951, er. No. 92,455

8 (Ilaims. (Cl. Zed-93.7) I

This nvention relates to a new and improved polymerization process and is particularly concerned with the use of a novel catalyst combination for preparing high molecular weight solid olyolefins, such as polypropylene, of high density and crystallinity. In a particular aspect the invention is concerned with the preparation of polypropylene and higher polyolefins having a high crystallinity and a high density using a particular catalyst combination which has unexpected catalytic activity.

This application is a continuation-in-part of our copending application, Serial No. 724,907, filed March 31, 1958, now abandoned.

Polyethylene has heretofore been'prepared by high pressure processes to give relatively flexible polymers having a rather high degree of chain branching and a density considerably lower than the theoretical density. Thus, pressures of the order of 500 atmospheres or more and usually of the order of 1000 to 1500 atmospheres are commonly employed. It has been found that more dense polyethylenes can be produced by certain catalyst combinations to give polymers which have very little chain branching and a high degree of crystallinity. The exact reason Why certain catalyst combinations give these highly dense and highly crystalline polymers is not readily understood. Furthermore, the activity of the catalysts ordinarily depends upon certain specific catalyst combinations, and the results are ordinarily highly unpredictable, since relatively minor changes in the catalyst combination often lead to liquid polymers rather than the desired solid polymers.

Catalyst compositions containing metal alkyls and transition metal compounds have been found to be effective for polymerizing olefins in low temperature, low pressure procedures and among the most effective catalysts are the mixtures of a trialkyl aluminum and either titanium trichloride or vanadium trichloride. When these catalysts are employed to polymerize propylene, the product has been found to have an inherent viscosity Within the range of about 1 to 3 and a crystallinity of about 70 to 75%. Also, such polymers have inadequate stiffness, thermal stability and softening point for many commercial applications unless stabilized and subjected to rather extensive extraction procedures for removal of oily and rubbery polymers.

It is an object of this invention to provide a novel and improved process for polymerizing propylene and higher u-monoolefins to form polymers of increased inherent viscosity and molecular weight and of substantially higher crystallinity. It is a particular object of this invention to provide a novel and improved process for polymerizing propylene in the presence of an improved catalyst composition containing a trialkyl aluminum and either titanium trichloride or vanadium trichloride. As a result of the use of this improved catalyst composition the inherent viscosity and crystallinity of the polymer are unexpectedly improved resulting in a polymer of substantially increased molecular weight and impact strength and in substantially increased clarity of molded objects. Other objects of this invention will be apparent from the description and claims which follow.

The above and other objects are attained by means of this invention, wherein a-monoolefins, either singly or in admixture, are readily polymerized to high molecular weight solid polymers by eiiecting the polymerization in the presence of a catalytic mixture containing an aluminum compound having the formula R Al wherein each R is a hydrocarbon radical containing 1 to 12 carbon atoms and selected from the group consisting of alkyl, aryl and aralkyl, a trihalide of a transition metal selected from the group consisting of titanium and vanadium, and a third component selected from the esters of carboxylic acids, lactones (intramolecular esters of carboxylic acids) and organic carbonates having the structural formulas:

ice

and

wherein R is selected from the group consisting of hydrogen, alkyl radicals containing 1 to 12 carbon atoms, phenyl, (CH COOR wherein n is a number from O to 4, and

-ooo1u R being an alkyl radical containing 1 to 4 carbon atoms and 'm being an integer of 1 to 4, and wherein R is selected from the group consisting of alkyl radicals containing l to 4 carbon atoms, phenyl, cycloheXyl, tetrahydrofuryl, S-acetoxyethyl and phenylalkyl wherein the alkyl radical contains 1 to 4 carbon atoms.

Among the specific compounds that can be used are ethyl acetate, methyl carbonate, butyl propionate, benzyl acetate, cyclohexyl formate, 'y-valerolactone, butyl oxalate,

methyl succinate, isopropyl phthalate, ethylene glycol diacetate, isobutyl phenylacetate, sec-butyl formate, ethyl n-caproate, butyl benzoate, ethyl laurate, tetrahytlrofurfuryl acetate, ethyl pelargonate, and the like.

Among the catalyst compositions that can be employed in practicing our invention are:

and butyl oxalate;

(8) Tripropyl aluminum, titanium tetraiodide and methyl succinate;

(9) Tributyl aluminum, vanadium tribromide and isopropyl phthalate;

(10) Triliexyl aluminum,

ethylene glycol diacetate; I

(11) Triethyl aluminum, titanium trichloride and isobutyl phenylacetate;

vanadium tetrabromide and (12) Trimethyl aluminum, titanium tetrachloride and secbutyl formate;

(13) Triethyl aluminum, titanium tribromide and ethyl n-caproate;

(14) Trimethyl aluminum, vanadium trichloride and butyl benzoate; I

(15) Tributyl aluminum, titanium trichloride and ethyl laurate;

(16) Triphenyl aluminum, titanium tetrachloride and tetrahydrofurfuryl acetate; and

(17) Triethyl aluminum, titanium trichloride and ethyl pelargonate.

The significantly improved properties of the polymers produced with the above catalyst were completely unexpected. The inventive process is carried out in liquid phase in an inert organic liquid and preferably an inert liquid hydrocarbon vehicle, but the reaction can be conducted in the absence of diluent. The process proceeds with excellent results over a temperature range of from C. to 250 C. although it is preferred to operate within the'range of from about 50 C. to about 150 C. Likewise, the reaction pressures maybe varied widely from about atmospheric pressure to very high pressures of the order of 20,000 p.s.i. or higher. A particular advantage of the invention is that pressures of the order of 30 to 1000 p.s.i. give excellent results, and it is not necessary to employ the extremely high pressures which were necessary heretofore. The liquid vehicle employed is desirably one which serves as an inert liquid reaction medium.

The invention is of particular importance in the preparation of highly crystalline polypropylene although it can be used for polymerizing mixtures of ethylene and propylene, the butenes and styrene as well as other inc-ID0110- olefins containing up to carbon atoms. The polypropylene produced in accordance with this invention possesses properties that are quite unexpected. The inherent viscosity and crystallinity of the polymer as well as the molecular weight, impact strength and clarity are substantially and unexpectedly improved. The high molecular weight, high density polymers of this invention are insoluble in solvents at ordinary temperatures but are partially soluble in such solvents as xylene, toluene or tetralin at elevated temperatures. These solubility characteristics make it possible to carry out the polymerization process under conditions wherein the polymer formed is soluble in the reaction medium during the polymerization and can be precipitated therefrom by lowering the temperature of the resulting mixture. The polypropylene produced by practicing this invention has a softening point above 155 C. and a density of 0.91 and higher. Usually, the

density of the polyproppylene is of the order of 0.91 to and can be used to form plates, sheets, films, or a variety 0 of molded objects which exhibit a higher degree of stiffness than do the corresponding high pressure polyolefins. The products can be extruded in the form of pipe or tubing of excellent rigidity and can be injection molded into a great variety of articles. The polymers can also be cold drawn into ribbons, bands, fibers or filaments of high elasticity and rigidity. Fibers of high strength can be spun from the molten polypropylene obtained according to this process. Other poly-a-olefins as well as copolymers of ethylene and propylene can also be prepared and have similarly improved properties.

As has been indicated above, the improved results obtained in accordance with this invention depend upon the particular catalyst combination. Thus, one of the components of the catalyst is an aluminum compound as defined hereinabove and preferably a trialkyl aluminum wherein the alkyl radicals contain from 1 to 12, preferably from 1 to 4, carbon atoms, for example, methyl, ethyl, propyl, butyl, and the like. R can also represent octyl, dodecyl, phenyi, benzyl and naphthyl radicals. The preferred trialkyl aluminum compounds are the lower alkyl derivatives, and the most preferred is triethyl aluminum. Another component of the catalyst composition is a trihalide of a transition metal selected from the group consisting of titanium and vanadium wherein the halogen is selected from the group consisting of chlorine, bromine and iodine. The third component of the catalyst composition has the structural formulas defined above.

The limiting factor in the temperature of the process appears to be the decomposition temperature of the catalyst. Ordinarily, temperatures from 50 C. to C. are employed, although temperatures as low as 0 C. or as high as 250 C. can be employed if desired. Usually, it is not desirable or economical to effect the polymerization at temperatures below 0 C., and the process can be readily controlled at room temperature or higher which is an advantage from the standpoint of commercial processing. The pressure employed is usually only suificient to maintain the reaction mixture in liquid form during the polymerization, although higher pressures can be used if desired. The pressure is ordinarily achieved by pressuring the system with the monomer whereby additional monomer dissolves in the reaction vehicle as the polymerization progresses.

The polymerization embodying the invention can be carried out batchwise or in a continuous flowing stream process. The continuous processes are preferred for economic reasons, and particularly good results are obtained using continuous processes wherein a polymerization mixture of constant composition is continousuly and progressively introduced into the polymerization zone and the mixture resulting from the polymerization is continuously and progressively withdrawn from the polymerization zone at an equivalent rate, whereby the relative concentration of the various components in the polymerization zone remains substantially unchanged during the process. This results in formation of polymer of extremely uniform molecular weight distribution over a relatively narrow range. Such uniform polymers possess distinct advantages since they do not contain any substantial amount of the low molecular weight or high molecular Weight formations which are ordinarily found in polymers prepared by batch reactions.

In the continuous flowing stream process, the temperature is desirably maintained at a substantially constant value within the preferred range in order to achieve the highest degree of uniformity. Since it is desirable to employ a solution of the monomer of relatively high concentration, the process is desirably effected under a pressure of from 30 to 1000 p.s.i. obtained by pressuring the system with the monomer being polymerized. The amount of vehicle employed can be varied over rather wide limits with relation to the monomer and catalyst mixture. Best results are obtained using a concentration of catalyst of from about 0.1% to about 2% by weight based on the weight of the vehicle. The concentration of the monomer in the vehicle will vary rather Widely depending upon the reaction conditions and will usually range from about 2 to 50% by weight. For a solution type of process it is preferred to use a concentration from about 2 to about 10% by weight based on the weight of the vehicle, and for a slurry type of process higher concentrations, for example up to 40% and higher, are preferred. Higher concentrations of monomer ordinarily increase the rate of polymerization, but concentrations above 5 to 10% by weight in a solution process are ordinarily less desirable because the polymer dissolved in the reaction medium results in a very viscous solution.

The molar ratio of aluminum compound to transition metal halide can be varied within the range of 1:05 to 1:2, and the molar ratio of halide to the third component of the catalytic mixture can be varied within the range of 1:1 to 1:01, but it will be understood that higher and lower molar ratios are within the scope of this invention. A particularly effective catalyst contains one mole of transition metal compound and 0.25 mole of the third component per mole of aluminum compound. The polymerization time can be varied as desired andwill usually be of the order of from 30 minutes to several hours in batch processes. Contact times of from 1 to 4 hours are commonly employed in autoclave type reactions. When a continuous process is employed, the contact time in the polymerization zone can also be regulated as desired, and in some cases it is not necessary to employ reaction or contact times much beyond one-half to one hour since a cyclic system can be employedby precipitation of the polymer and return of the vehicle and unused catalyst to the charging zone wherein the catalyst can be replenished and additional monomer introduced.

The organic vehicle employed can be an aliphatic alkane or cycloalkane such as pentane, hexane, heptane or cyclohexane, or 'a hydrogenated aromatic compound such as tetrahydronaphthalene or decahydronaphthalene, or a high molecular weight liquid paraffin or mixture of parafiins which are liquid at the reaction temperature, or an aromatic hydrocarbon such as benzene, toluene, xylene, or the like, or a halogenated aromatic compound such as chlorobenzene, chloronaphthalene, or orthodichlorobenzene. The nature of the vehicle is subject to considerable variation, although the vehicle employed should be liquid under the conditions of reaction and relatively inert. The hydrocarbon liquids are desirably employed. Other solvents which can be used include ethyl benzene, isopropyl benzene, ethyl toluene, n-propyl benzene, dlethyl benzenes, mono and dialkyl naphthalenes, n-pentane, n-octane, isooctane, methyl cyclohexane, tetralin, decalin, and any of the other well known inert liquid hydrocarbons.

The polymerization ordinarily is accomplished by merely admixing the components of the polymerization mixture, and no additional heatis necessary unless it is desired to eiiect the polymerization at an elevated temperature in order to increase the solubility of polymeric product in the vehicle. When the highly uniform polymers are desired employing the continuous process wherein the relative proportions of the various components are maintained substantially constant, the temperature is desirably controlled within a relatively narrow range. This is readily accomplished since the solvent vehicle forms a high percentage of the polymerization mixture and hence can be heated or cooled to maintainthe temperature as desired.

A particularly eifective catalyst for polymerizing propylene and other a-monoolefins in accordance with this invention is a mixture of triethyl aluminum, titanium trichloride and ethylene glycol diacetate. The importance of the third component of this reaction mixture is evident from the fact that the presence of .the third component makes possible the production of polymers of substantially improved properties.

The invention is illustrated by the following examples of certain preferred embodiments thereof.

Example 1 In a nitrogen-filled dry box, a total of 2 g. of catalyst was added to a 500-ml. pressure bottle containing 100 ml. of dry heptane. The catalyst was made up of triethylaluminum, titanium tetrachloride and ethyl pelargonate in a molar ratio of 2:2: 1. The pressure bottle was then attached to a source of propylene, and the reaction mixture was agitated, heated to 75 C. and maintained under 30 psi. propylene pressure for 6 hours. At the end of this time, the bottle was removed from the propylene source, dry isobutyl alcohol was added to deactivate the catalyst, and then the polymer was washed with hot, dry isobutanol to remove the catalyst residues. The yield of highly crystalline polypropylene was 14.2 g. This polymer had an inherent viscosity in tetralin at 145 C. of 2.10 and a density of 0.908.

When a control run was made using only the triethylaluminum and titanium tetrachloride omitting the ethyl pelargonate, very little crystalline polypropylene was formed under these conditions.

6 Example 2 Inside a nitrogen-filled dry box, a 285-rnl. stainless steel autoclave was loaded with 2 g. of three-component catalyst comprising a 1:1:0.25 molar ratio of triethylaluminum, titanium trichloride and sec butyl formate and ml. of dry mineral spirits (B.P. 197 C.). The autoclave was sealed, placed in a rocker, and 100 ml. (51 g.) of dry, liquid propylene was added. Rocking was initiated, and the mixture was heated to 85 C. and maintained at this temperature for 6 hours. The polymer was worked up as described in Example 1 to give a yield of 40 g. of highly crystalline polypropylene having an inherent viscosity of 2.55 in tetralin at C. When hydrogen was admitted to the polymerizationvessel and was maintained there at 50 p.s.i. partial pressure, the inherent viscosity of the product was 1.90. An increase in the hydrogen pressure to 500 psi. in a similar experiment produced a very low molecular weight crystalline polypropylene of inherent viscosity 0.40.

Example 3 The procedure of Example 2 was used to polymerize propylene with no solvent present. One hundred grams of liquid propylene monomer was used and within the 6-hour reaction period at 85 C., a 98.5-g. yield of highly crystalline polypropylene of inherent viscosity of 3.45 was obtained.

Example 4 Example 5 The procedure of Example 2 was used to polymerize a SO-g. charge of styrene using 0.75 g. of catalyst comprised of triethylaluminum, vanadium trichloride and ethyl ncaproate. A 45-g. yield of crystalline polystyrene was obtained. This polymer had an inherent viscosity of 2.68 and a crystalline melting point (powder) of 231 to 238 C.

Example 6 In a nitrogen-filled dry box, a 7-oz. tapered pressure bottle was charged in order with 40 ml. of dry benzene, 20 g. of 4-methyl-l-pentene and 1 g. of a catalyst consisting of triethylalurninurn, vanadium tetrachloride and methyl succinate in a Inolarratio of 1:321. The bottle was capped, placed in a rotating wheel in a constant-temperature water bath maintained at 70 C. and was allowed to remain under these conditions for 24 hours. At the end of this period, the bottle was removed, allowed to cool and opened. The polymer was dissolved in hot xylene and precipitated by the addition of dry isobutanol to the xylene solution in a Waring Blender. The polymer was washed several times with hot isobutanol and was dried. The crystalline poly-(4-methyl-1-pentene) weighed 17.2 g. and melted at 200 to 205 C. (powder).

Allylbenzene, vinylcyclohexane, butadiene, isoprene, and 3-phenyl-1-butene were readily polymerized by this procedure to give solid polymers.

Other compoundswhich gave similar results when used in place of methyl succinate include ethyl acetate, ethyl laurate and isobutyl phenlacetate.

Example 7 The procedure of Example 2 was followed except that the catalyst charge was 1 g. of a mixture of triethylaluminum, titanium trichloride and ethylene glycol diacetate in a molar ratio of 12120.5. No solvent was employed and the polymerization temperature was 85 C. The

amass? crystalline polypropylene obtained had a density of 0.913 and an inherent viscosity of 2.40.

Other esters which may be used in place of ethylene glycol diacetate to give similar results include methyl carbonate, benzyl acetate, -y-valerolactone, butyl oxalate, cyclohexyl formate, butyl benzoate, tetrahydrofurfuryl acetate and isopropyl phthalate.

The diluents that are employed in practicing this invention can be advantageously purified prior to use in the polymerization reaction by contacting the diluent, for example in a distillation procedure or otherwise, with the polymerization catalyst to remove undersirable impurities. Also, prior to such purification of the diluent the catalyst can be contacted advantageously with polymerizable a-monoolefins.

Thus, by means of this invention polyolefins such as polypropylene are readily produced using a catalyst combination whose improved eifectiveness could not have been predicted. The polymers thus obtained can be extruded, mechanically milled, cast or molded as desired. The polymers can be used as blending agents with relatively more flexible polyhdrocarbons to give any desired combination of properties. The polymers can also be blended with antioxidants, stabilizers, plasticizers, fillers, pigments, and the like, or mixed with other polymeric materials, waxes and the like.

From the detailed disclosure of this invention it is quite apparent that in this polymerization procedure a novel catalyst, not suggested in prior art polymerization procedures, is employed. As a result of the use of this novel catalyst, it is possible to produce polymeric hydrocarbons, particularly polypropylene, having properties not heretofore obtainable. For example, polypropylene prepared in the presence of catalyst combinations within the scope of this invention is substantially free of rubbery and oily polymers, and thus it is not necessary to subject such polypropylene of this invention to extraction procedures in order to obtain a commercial product. Also, polypropylene produced in accordance with this invention possesses unexpectedly high crystallinity, an unusually high softening point and outstanding thermal stability. Such polypropylene also has a Very high stiffness as a result of the unexpectedly high crystallinity. The properties imparted to polypropylene prepared in accordance with this invention thus characterize and distinguish this polypropylene from polymers prepared by prior art polymerization procedures.

The novel catalysts defined above can be used to produce high molecular weight crystalline polymeric hydrocarbons. The molecular weight of the polymers can be varied over a wide range by introducing hydrogen to the polymerization reaction. Such hydrogen can be introduced separately or in admixture with the olefin monomer. The polymers produced in accordance with this invention can be separated from polymerization catalyst by suitable extraction procedures, for example, by washing with water or lower aliphatic alcohols, such as methanol.

I The catalyst compositions have been described above as being effective primarily for the polymerization of a-monoolefins. These catalyst compositions can, however, be used for polymerizing other ot-olefins, and it is not necessary to limit the process of the invention to monoolefins. Other e-olefins that can be used are butadiene, isoprene, 1,3-pentadiene and the like.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, variations and modifications can be effected within the spirit and scope of this invention as described hereinabove and as defined in the appended claims.

We claim:

1. In the polymerization of propylene to form solid crystalline polymer, the improvement which comprises effecting the polymerization in the presence of a catalytic mixture of triethyl aluminum, titanium trichloride and ethylene glycol diacetate.

2. The method according to claim 1 wherein vanadium trichloride is used in the catalyst mixture in place of titanium trichloride.

3. The method according to claim 1 wherein trimethyl aluminum is used in the catalyst mixture in place of triethyl aluminum.

4. As a composition of matter, a catalytic mixture for the polymerization of propylene of triethyl aluminum, titanium trichloride and ethylene glycol diacetate.

5. A composition according to claim 4 wherein vanadium trichloride is used in the catalyst mixture in place of titanium trichloride.

6. A composition according to claim 4 wherein trimethyl aluminum is used in the catalyst mixture in place of triethyl aluminum.

7. In the polymerization of OL-l'l1OI1001fiIllC hydrocarbon material containing 3 to 10 carbon atoms to form solid crystalline polymer, the improvement which comprises catalyzing the polymerization with a catalytic mixture containing an aluminum compound having the formula R Al wherein R is a hydrocarbon radical containing 1 to 12 carbon atoms selected from the group consisting of alkyl, aryl and aralkyl, a halide of a transition metal selected from the group consisting of titanium and vanadium, and an ester having the formula RCOOR wherein R has the formula -(CH ),,COOR wherein n is a number from 0 to 4 and R and R are alkyl radicals containing 1 to 4 carbon atoms.

8. As a composition of matter, a polymerization catalyst containing an aluminum compound having the formula R Al wherein R is a hydrocarbon radical containing 1 to 12 carbon atoms selected from the group consisting of alkyl, aryl and aralkyl, a halide of a transition metal selected from the group consisting of titanium and vanadium, and an ester having the formula RCOOR wherein R has the formula (CH ),,CO0R wherein n is a numher from O to 4 and R and R are alkyl radicals containing 1 to 4 carbon atoms.

2,905,645 Anderson et al Sept. 22, 1959 Field et al Dec. 20, 1960 

7. IN THE POLYMERIZATION OF A-MONOOLEFINIC HYDROCARBON MATERIAL CONTAINING 3 TO 10 CARBON ATOMS TO FORM SOLID CRYSTALLINE POLYMER, THE IMPROVEMENT WHICH COMPRISES CATALYZING THE POLYMERIZATION WITH A CATALYTIC MIXTURE CONTAINING AN ALUMINUM COMPOUND HAVING THE FORMULA R3AL WHEREIN R IS A HYDROCARBON RADICAL CONTAINING 1 TO 12 CARBON ATOMS SELECTED FROM THE GROUP CONSISTING OF ALKYL, ARYL AND ARALKYL, A HALIDE OF A TRANSITION METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM AND VANADIUM, AND AN ESTER HAVING THE FORMULA RCOOR1 WHEREIN R HAS THE FORMULA -(CH2)NCOOR2 WHEREIN N IS A NUMBER FROM 0 TO 4 AND R1 AND R2 ARE ALKYL RADICALS CONTAINING 1 TO 4 CARBON ATOMS. 